The right AC installation depends mostly on what your home already has. If you have a furnace with ductwork in decent shape, a central split system or a heat pump on that duct system is usually the cleanest choice. With no ducts, a ductless mini split is the common answer, and for a single room a window or through-wall unit may be all you need. Whatever the type, the size should come from a load calculation, not the square footage or the old unit's label.
For a fuller look at every category, see types of air conditioners compared.
Which type of AC installation fits your home?
Start with your home's situation, not the equipment.
| Your home | Usually the best fit | Why | Watch for |
|---|---|---|---|
| Ducts plus a gas furnace in decent shape | Central split AC, or a heat pump for dual fuel | Uses the existing furnace blower and ducts | Coil must match the furnace; ducts may need sealing |
| Ducts plus an old electric furnace or air handler | Heat pump with a new air handler | Heats far more efficiently than electric resistance | Electrical capacity for backup strip heat |
| No ducts, older home with a boiler and radiators | Ductless mini split, or a small-duct high-velocity system | Adds cooling without tearing open walls | Head placement, condensate routing, wall appearance |
| No ducts, electric baseboard heat | Ductless heat pump (mini split) | Cools and replaces costly resistance heat | Enough zones to reach closed-off rooms |
| One room, addition, garage or sunroom | Single-zone mini split, or a window or through-wall unit | No need to extend ducts | Wall sleeve size; a dedicated circuit for larger units |
| Renting or no permanent changes allowed | Window or portable unit | Removable, no refrigerant work | Window type, weight support, outlet rating |
If you're torn between straight cooling and a heat pump, heat pump vs air conditioner walks through climate and fuel costs.
Comfort problems that trace back to the install
Most AC complaints in the first few years come from installation choices, not bad equipment.
| Comfort problem | Install mistake that causes it |
|---|---|
| Cold but clammy house, short run times | Oversized unit chosen by square footage or copied from the old one |
| Upstairs never cools on hot afternoons | Undersized ducts or returns, or no balancing after install |
| Weak airflow, noisy registers | Blower not set to the new equipment, or high duct static pressure |
| Ice on the indoor coil or refrigerant lines | Wrong refrigerant charge or too little airflow over the coil |
| Water leaks at the air handler or a mini split head | Drain line with no slope or trap, or no float switch |
| Mini split room too cold while others stay warm | Head sized too large for the room, or too few zones |
| Window unit drips indoors or rattles | Unit not tilted to drain, no support bracket, gaps not sealed |
What to check before you get AC installation bids
You can collect most of this without tools, and it helps you judge which contractors actually looked.
- The data plate on the old outdoor unit. Photograph it for the model and serial numbers, refrigerant type, and electrical ratings (minimum circuit ampacity and maximum breaker). R-22 means any leak repair will be expensive, since US production ended on January 1, 2020.
- The furnace or air handler label. Its age and blower type determine whether the existing indoor side can be kept.
- Breaker sizes. Note the AC breaker and the main breaker rating from the panel door. Don't remove the panel cover.
- Ducts you can see. Look for crushed flex, disconnected joints and missing insulation in the attic or basement, and count the returns.
- Wall space and outlets. For a mini split, note where heads could go and where the outdoor unit could sit. For a window unit, measure the opening and check that the outlet matches the plug.
- Comfort notes. List rooms that run hot, humidity problems and anything that changed since the last system, like new windows or insulation.
Don't open the outdoor unit's electrical panel. The capacitor inside can hold a charge with the power off, and the refrigerant circuit should only be opened by a technician with EPA Section 608 certification.
How each type of AC is installed
These are the short versions. The linked guides go step by step.
Central split system
The old refrigerant is recovered, then the condenser goes on a level pad and the matched evaporator coil sits on top of the furnace. The refrigerant line set is reused or replaced, brazed, pressure tested with nitrogen and pulled into deep vacuum before the system is charged and the airflow set. Expect a disconnect at the outdoor unit, a new condensate drain and a permit inspection. The full sequence is in central AC installation in depth.
Heat pump
The install looks almost identical to a central AC, with a heat pump outdoors and either a matched coil on a gas furnace (dual fuel) or a new air handler with backup heat strips. Extra steps include outdoor thermostat or balance point settings, a raised pad or stand in snowy areas, and a larger circuit if the air handler has strips.
Ductless mini split
The installer mounts each indoor head on a bracket, drills a hole of about 3 inches through the wall for the line set, communication cable and drain, and sets the outdoor unit on a pad or wall bracket. The lines are flared or brazed, pressure tested and evacuated, and condensate either drains by gravity or through a small pump. The mini split installation guide covers zone sizing and head placement.
Window and through-wall units
A window unit is a homeowner job with care: use a support bracket, tilt it slightly outward if the manual says to, seal the side panels, and plug it directly into a properly rated outlet with no extension cord. Larger units may need a 230-volt dedicated circuit, which is electrician work. A through-wall unit needs a sleeve cut into an exterior wall, and on a bearing wall that can mean framing a header. See the best window air conditioners for model choices.
How big an AC do you need?
Central systems and heat pumps should be sized from an ACCA Manual J load calculation using insulation, windows, orientation and local climate. Oversized units short-cycle and leave humidity behind; undersized ones run nonstop on the hottest days. The guide to what size AC unit you need explains how sizing works.
Refrigerant: R-410A and the new A2L systems
R-410A equipment is being phased out under EPA rules, and new residential central ACs, heat pumps and many mini splits now use A2L refrigerants such as R-454B and R-32. A2L refrigerants are mildly flammable, so installers need compatible tools and training, and some equipment includes leak sensors. Indoor and outdoor components must be designed for the same refrigerant, which is one more reason to replace them as a matched set. Ask each bidder which refrigerant the proposed system uses.
What affects AC installation cost
The type you choose sets the baseline. Window units are the cheapest by far, single-zone mini splits sit in the middle, and central air or a heat pump costs more, especially if ducts have to be added. For typical ranges see the central air pricing and mini split installation cost guides.
Within a type, these move the number:
- Capacity and efficiency. Larger tonnage and higher SEER2 cost more; variable-speed units sit at the top tier.
- Ductwork. Sealing or adding returns is modest; new ducts in a home without them is often the largest single cost.
- Number of zones. Each mini split head adds equipment, line set and labor.
- Electrical. A new circuit, disconnect or panel upgrade.
- Access, permits and local labor rates.
- Incentives. Utility and state rebates often apply to heat pumps and high-efficiency units. Federal tax credit rules have changed recently, so check what's in effect.
Repair or replace your AC?
Use the 50 percent rule as a starting point: if the repair costs more than half of a comparable new system, replacement usually wins. Lean toward replacing when the system is past 12 to 15 years, the compressor has failed, there's a refrigerant leak on an R-22 unit, or you've had repeated breakdowns. A failed capacitor, contactor or fan motor on a younger system is usually worth repairing. The AC repair guide covers diagnosis.
How to vet an AC installer and compare bids
Ask each contractor:
- Will you run a Manual J load calculation and share it?
- What's the AHRI reference number for the exact outdoor unit and indoor coil or air handler?
- Which refrigerant does the system use, and will you reuse or replace the line set?
- Who pulls the permit?
- What startup readings (superheat or subcooling, static pressure) will you record and give me?
- What labor warranty do you offer in writing, and who registers the manufacturer warranty?
- Are you licensed and insured, and EPA Section 608 certified?
Red flags:
- Sizing by square footage or by copying the old unit's tonnage, with no load calculation
- An outdoor unit quoted with no matching indoor coil
- Skipping the permit
- Cash only, or a large deposit before equipment is ordered
- Pressure to sign the same day
- Bids that list a brand and tonnage but no model numbers
Compare bids by capacity, efficiency rating and scope (pad, line set, drain, thermostat, disposal, permit). A low price often hides a missing coil or a skipped permit.
Frequently Asked Questions
How long does AC installation take?
A central AC or heat pump replacement on existing ducts usually takes one day. A single-zone mini split often takes a day, and multi-zone systems one to three days. A window unit takes an hour or two. Adding ductwork to a home that never had it can take several days.
Do I need a permit to install a new AC?
For central air, heat pumps and mini splits, most jurisdictions require a mechanical permit, and often an electrical one, followed by an inspection. The installer normally pulls it. Plug-in window and portable units don't need a permit, though a new dedicated circuit for a large window or through-wall unit may.
Can I install an air conditioner myself?
A plug-in window unit, yes, with a helper and a proper support bracket. Central air, heat pumps and most mini splits involve refrigerant, which requires EPA Section 608 certification, plus high-voltage wiring and permits. DIY installation of those systems usually voids the manufacturer warranty.
Is a mini split better than central air?
Neither is better everywhere. Central air makes the most sense when the house already has ducts in good shape. A mini split avoids duct losses and gives room-by-room control, which makes it the better fit for homes without ducts, additions and problem rooms. Many homes end up using both.
Should I replace my furnace at the same time as my AC?
Consider it if the furnace is past about 12 to 15 years old. The AC's indoor coil sits on the furnace and the furnace blower moves the air for both, so the parts need to match. Doing both together usually costs less than two separate jobs. A newer furnace can stay if the new coil is rated to match it.
What SEER2 rating should I look for?
The federal minimum for most new residential split-system central air conditioners is 13.4 SEER2 in northern states and 14.3 SEER2 in the Southeast and Southwest. Higher ratings cost more upfront and pay back faster where the AC runs many hours a year. Check that the rating applies to the exact indoor and outdoor combination you're buying.